1. Field of the Art
This invention relates to a process for producing a graft copolymer having the main chain of a copolymer comprising an .alpha.-olefin and a dialkenylbenzene and the side chain of a polymer of an anion or radical polymerizable monomer.
2. Prior Art
A polyolefin modified with a polymerizable aromatic hydrocarbon type monomer such as styrene and its derivative is endowed with affinity for aromatic hydrocarbon polymers which has not been inherently possessed by a polyolefin. Accordingly, such modification is utilized for improvement in adhesiveness or compatibility with aromatic hydrocarbon polymers. Also, in some cases, it becomes possible to disperse the modified polyolefin itself into a matrix resin, whereby impact resistance and other characteristics of the matrix resin can be improved.
Also, a polyolefin modified with a polymerizable monomer having a polar group in the molecule such as unsaturated carboxylates and nitriles is endowed with adhesiveness with polar substances, miscibility with other polar resins. Accordingly, a polyolefin thus modified is used for wide uses combined with other substances.
As the method for modification method to obtain such modified polyolefins, there have been done a large number of attempts to modify the polyolefins made by use of Ziegler-Natta type catalysts into random copolymers, block copolymers or graft copolymers by use of vinyl aromatic compounds, conjugated diene compounds, polar group containing polymerizable monomers, etc.
For example, the following production methods have been known.
i) The method in which an .alpha.-olefin and another copolymerizable monomer are subjected to random copolymerization by use of one kind of catalyst comprising the Ziegler-Natta type catalyst (the case when the copolymerizable monomer is a nitrogen-containing or oxygen-containing vinyl monomer: J. Polymer Sci., Part C No. 22, 157 (1968), U.S. Pat. No. 3,492,277, Japanese Patent Publication No. 37,756/1973, Japanese Laid-Open Patent Publications No. 116,710/1980, No. 80,413/1984 and No. 80,414/1984, Makromol. Chem. Macromol. Symp., 3, 193 (1986); the case when the copolymerizable monomer is a conjugated diene: J. Polymer Sci., Polym. Chem. Ed., 10, 3027 (1972), Makromol. Chem. 179, 2173 (1978); the case when the copolymerizable monomer is a styrene type monomer: Japanese Laid-Open Patent Publication No. 26011/1985).
These methods are generally inherent in low polymerization activity and the polymer yield may be sometimes extremely poor. Also, it is difficult to control the composition and distribution of the comonomer in the copolymer chain, and therefore a modified polyolefin copolymer controlled in the polymer structure can be obtained with difficulty. Particularly, since it is difficult for the copolymer to include segment which is produced by continuously polymerized comonomer units themselves, these methods are not adequate when it is desired to obtain a modified polyolefin having both the characteristics of the .alpha.-olefin polymer and the characteristics of the homopolymer of the comonomer itself.
ii) The method for modifying polyolefin by block copolymerization of an .alpha.-olefin with other various polymerizable monomers.
As such modification method, first the following methods have been attempted.
a) A method for producing a block copolymer of an .alpha.-olefin and tetrahydrofuran wherein by using a specific vanadium-based Ziegler-Natta type catalyst a living polymer of an .alpha.-olefin is produced and then a specific transformative treatment is applied to the active terminal end of the living polyolefin to form a terminal carbocation which is to effect the block copolymerization (Japanese Laid-Open Patent Publications No. 196,317/1984 and No. 252,623/1985). A method for producing a block copolymer of an .alpha.-olefin and methyl methacrylate by using the same catalyst and forming a radical group at the active terminal end of the living polyolefin, thereby polymerizing methyl methacrylate. (Makromol. Chem. 186, 11 (1985)). There is also a method for obtaining a block copolymer of an .alpha.-olefin and styrene by adding a halogen to the active terminal end of the same living polyolefin and carrying out the coupling reaction between this product and a living polystyryl potassium (C. C. Price ed., "Coordination Polymerization" Plenum Pub., New York (1983), p. 246).
b) Further, as a method similar to the above method, there has been also proposed a method for obtaining a block copolymer of an .alpha.-olefin and styrene by adding a halogen to the terminal double bond of a polyolefin obtained by the so-called Kaminsky type Ziegler-Natta type catalyst, and then carrying out the coupling reaction of the product with a living polystyryl lithium (Japanese Laid-Open Patent Publication No. 158,709/1987).
However, according to these methods a) and b), .alpha.-olefin is polymerized by use of a specified Ziegler-Natta type catalyst, and therefore the block segment of the polyolefin produced would be specialized in the polymer structure. Accordingly, the block copolymer obtained by these methods would be limited in uses. For example, when propylene is used as .alpha.-olefin in the method of a), the structure of the polypropylene chain becomes to have the syndyotactic structure, whereby no block copolymer with polypropylene having useful isotactic structure would be obtained. On the other hand, the polyolefin obtained by the method of b) would have narrow molecular weight distribution, and therefore this method would not be suitable when a polymer with broad molecular weight distribution is required. Further, both of the methods a) and b) must be performed according to a plural number of complicated reaction steps and under special conditions of extremely low temperature, etc., thus involving problems with respect to economy such as catalyst cost, process cost, etc. along with block efficiency.
c) As a method to utilize the active terminal end of a polyolefin, there also exists the method for obtaining a block copolymer by polymerizing an .alpha.-olefin by use of a conventional Ziegler-Natta type catalyst, and then polymerizing an acrylate or methacrylate in the presence of specific catalyst species such as an organic phosphorus compound or a tertiary amine and a benzyl halide (Japanese laid-Open Patent Publications No. 38,594/1977, No. 39,786/1977, No. 63,987/1977 and No. 37,791/1978). However, this method would involve the problems such that the polyolefin inactivated may be partially formed in the former stage polymerization and that the comonomer species available in the latter stage polymerization is limited.
d) There has been also attempted a method for obtaining a block copolymer of polyolefin and polystyrene or polybutadiene according to the so-called active site transformation method between the anionic polymerization active site and the Ziegler-Natta type polymerization active site (Japanese Laid-Open Patent Publication No. 20,918/1985, Eur. Polymer J., 17, 1175 (1981), Makromol. Chem., 181, 1815 (1980)). However, these methods have various problems such as lowering in catalyst activity and lowering in block efficiency due to low active site transformation efficiency, and also difficulty in obtaining a copolymer having a desired controlled molecular weight (particularly an anionic polymer chain of high molecular weight), etc.
iii) The method in which other various polymeric monomers are grafting onto a polyolefin obtained by use of the Ziegler-Natta type catalyst.
The method for producing a modified polyolefin by grafting a radical polymerizable monomer onto a polyolefin produced by the Ziegler-Natta type catalyst is a modification method which has been attempted in a large number for many years (Japanese Patent Publication No. 18,118/1971, etc.). For this radical grafting reaction, organic peroxides, O.sub.3 (ozone), UV-ray, radiation, etc. are used as the radical generation source. Accordingly, this reaction may sometimes require a special ray source or device, and cannot be a general method in some cases. The method by use of an organic peroxide has no problem with respect to the device as mentioned above, but it involves many problems such as susceptibility of the trunk polymer, i.e. a polyolefin, on which grafting is to be effected to polymer scission, susceptibility to gellation, readiness in formation of homopolymer of the polymerizable monomer to be grafted (lowering in grafting efficiency), difficulty in control of the molecular weight of the graft side chain (these are recognized commonly in the radical grafting methods), whereby a graft-modified polyolefin having desired characteristics can be obtained with difficulty.
As an alternative method for such radical grafting method, there has been also made an attempt to obtain a copolymer having polymer chains of an .alpha.-olefin and an anion-polymerizable monomer by combining the Ziegler-Natta type polymerization by use of a Ziegler-Natta type catalyst and the anionic polymerization by use of an anion polymerization initiator (Japanese Patent Publication No. 32,412/1971). However, only by combining simply polymerizations of two different types, because these polymerization active species themselves are different from each other, it would be difficult to form a copolymer with an intervening chemical bond between the polyolefin and the polymer of an anion-polymerizable monomer. That is, the product obtained may be mostly a mixture of the respective homopolymers formed by the two types of polymerizations (see Comparative Example 1 shown below).
An attempt has been also made to improve this problem (Japanese Laid-Open Patent Publications No. 54,712/1987 and No. 54,713/1987). However, according to these methods, the poly-.alpha.-olefin formed by the Ziegler-Natta type polymerization is subjected to a complicated specific post-treatment, namely removal of the organic aluminum compound used in the Ziegler-Natta type polymerization by washing with an inert hydrocarbon solvent, and further to the contact treatment between the poly-.alpha.-olefin and an organic lithium compound. Further, after unreacted organic lithium compound is removed by washing, finally copolymerization with styrenes or polar group containing vinyl monomers must be carried out, thus involving cumbersome operations.